This invention relates to a method of manufacturing an electron gun having a beaded unit comprising a number of electrodes connected to electric leads and secured to beading rods, and a base comprising a number of pins, which beaded unit and base are connected by means of a sub-assembly of securing means and an insulating plate.
The invention also relates to an electron gun having a beaded unit comprising a number of electrodes connected to electric leads and secured to beading rods, and a base comprising a number of pins, which beaded unit and base are connected by means of a sub-assembly of securing means and an insulating plate, to a display device provided with such an electron gun and to a sub-assembly for use in such an electron gun.
Such display devices may be cathode ray tubes for use in, for instance, television sets and computer monitors.
An electron gun as described above is disclosed in U.S. pat. No. 4,082,977. The known electron gun according to said patent is provided with securing means for connecting the beaded unit to the base. Said securing means comprise an insulating plate with a number of apertures. Some of the apertures in the insulating plate correspond to the pins of the base. These apertures are provided with a metal eyelet, secured to the insulating plate, for instance, by clamping. These eyelets are used for connecting the insulating plate to the base, for instance, by welding the pins to the eyelets. The remaining apertures in the insulating plate are also provided with eyelets and are meant to engage the standards of the beaded unit of the electron gun, in a way that resembles male-female socket components. It is also possible to provide the insulating plate with electric contacts. Although said patent describes an electron gun with a connection between the beaded unit and the base, it also has some drawbacks. Primarily, this construction is used for making the connection between the standards of the beaded unit and the base; the electric leads from the electrodes of the beaded unit are mostly directly connected to the pins of the base or to the eyelets. Moreover, the construction is rather complicated, including a large number of eyelets in the insulating plate.
Conventional electron guns used in cathode ray tubes (CRTs) comprise a number of electrodes which are positioned one behind the other, starting from the (at least one) cathode and ending at the anode, which is the final accelerating electrode. If the CRT is a monochromatic tube, only one cathode is present; in the well-known color CRT, the electron gun will generate three electron beamsxe2x80x94one for each color of electroluminescent material on the screenxe2x80x94i.e, the electron gun has three cathodes. The electrodes in an electron gun are mechanically interconnected during the beading process, by partly embedding the electrodes in a number of beading rods, resulting in the sub-assembly that is usually referred to as the beaded unit. This beaded unit has to be secured to the base, which base normally comprises a glass base plate and a number of electric leads, commonly referred to as the pins.
The step in the known manufacturing process of electron guns, in which the beaded unit is secured to the base, is time-consuming and, as a consequence, rather expensive. Moreover, since it is a largely manual process, it also introduces spreads in the quality of the final product.
It is an object of the invention to provide a method of manufacturing an electron gun, which is improved with respect to the method as described in the opening paragraph, and in which the above-mentioned problems will be largely reduced or even solved.
According to the invention, a method for manufacturing an electron gun that realizes this object is characterized in that
a pattern of openings is provided in a planar element, thereby forming a number of securing means, still planar-shaped, attached to a remainder of the planar element,
portions of said securing means are bent out of the plane of the planar element, to provide the securing means with a three-dimensional shape,
the securing means are inserted into a plurality of first apertures of the insulating plate and secured therein to form the sub-assembly
the sub-assembly of securing means and insulating plate is disconnected from the remainder of the planar element, and
the sub-assembly of securing means and insulating plate is connected to the beaded unit and the base, to form the electron gun.
For connecting the beaded unit of the electron gun to its base, this method uses an insulating plate provided with apertures which engage a number of securing means. These securing means may be fixed to the insulating plate by twisting the ends of the securing means, thus forming said sub-assembly. These securing means, positioned between the beaded unit and the base, are connected at one side to the beaded unit and at the other side to the pins of the base. Most current electron guns do not comprise this sub-assembly of securing means and insulating plate. In these electron guns, the beaded unit is directly connected to the pins of the base. This part of the process has to be done largely by hand and is very difficult to mechanize, so that it is a time-consuming and expensive step in the manufacturing process of electron guns. Besides these aspects, the manual treatment of an electron gun at this stage of the production process introduces an undesired spread of some important mechanical parameters of the electron guns that partly determine the performance in the final product. The increasingly stricter requirements imposed on the performance of electron gunsxe2x80x94spot sizes, mechanical stability, high voltage behaviorxe2x80x94makes it necessary to improve the connection between the beaded unit and the base in order to fulfill the requirements for future designs of electron guns.
The invention is based on the recognition that the introduction of an intermediate sub-assembly of securing means and insulating plate provides a manufacturing method that will largely overcome the drawbacks of the known method. This is motivated by the fact that the sub-assembly of securing means and insulating plate can easily be made with a high accuracy. The process in which this sub-assembly is connected to the beaded unit and to the base, for instance, by means of a welding process, can then be done in a mechanized way with a much higher accuracy and a much higher speed than manual mounting of these components. The higher accuracy of this process improves the performance of the gun in the CRT. For instance, one of the items that are improved is the phenomenon which is usually referred to as delta-Vco. Delta-Vco, is understood to be the difference in cut-off voltage between the three cathodes of a color CRT, causing an unbalance in the drive of the three electron beams, leading to a shift in color at different brightness levels. This phenomenon is clearly negatively influenced by manual actions during the manufacturing process. Another advantage of this method is that the mechanized method of interconnecting the beaded unit to the base can lead to an electron gun that is at least 2 mm shorter than electron guns that are manufactured without said sub-assembly.
An embodiment of the method according to the present invention is characterized in that the insulating plate has a plurality of second apertures for leading through the electric leads of a number of the electrodes. An embodiment like this makes it possible to guide electric leads through these apertures in the insulating plate, so that the electric leads can be connected, for instance by welding, to the securing means, which themselves are connected to the pins of the base. In this way, an electrical connection is formed from the outside of the display device to the proper electrode. Consequently, the securing means have to be electrically conductive, and are preferably made of metal.
A further embodiment of the method according to the present invention is characterized in that the apertures in the insulating plate are funnel-shaped. The funnel-shaped apertures make the assembly process easier, because both the securing means and the electric leads will be more easily guided through the apertures in the insulating plate.
A further embodiment of the method according to the present invention is characterized in that the first apertures in the insulating plate are tapered in a direction away from the base and the second apertures are tapered in a direction towards the base. Making the tapers in these directions is preferred, because the securing means enter the insulating plate from the side of the base, while the electric leads enter the securing means from the side of the beaded unit.
A still further embodiment of the method according to the present invention is characterized in that the pattern of openings in the planar element is obtained by stamping the openings in the planar element. Stamping the opening in the planar element has a great advantage from an industrial point of view. It is an easy method that can be performed in a mechanized way with high accuracy and at high speed. Besides, it is possible to produce these planar elements from a tape of metal on a reel. Of course, these planar elements may be produced by using other manufacturing methods like etching, which yields products with high accuracy and without mechanical stresses, but an etching process will be more expensive.
The invention also relates to an electron gun having a beaded unit comprising a number of electrodes connected to electric leads and secured to beading rods, and a base comprising a number of pins, which beaded unit and base are connected by means of a sub-assembly of securing means and an insulating plate, characterized in that the insulating plate is provided with a plurality of first apertures that let through the securing means, and a plurality of second apertures that let through the electric leads of a number of the electrodes, said electric leads being connected to the securing means which are connected to pins of the base.
Furthermore, the invention relates to a display device provided with such an electron gun. The invention also relates to a sub-assembly for use in such an electron gun.
These and other aspects of the invention are apparent from and will be elucidated by way of non-limitative examples with reference to the drawings and the embodiments described hereinafter.